The initial design was made of 5mm and 3mm plastic which is difficult to bend and process, requiring tight tolerances and lots of manual labor.
Last week we've been trying to optimize the design for thin plastic and make it lasercut-only, with rivets for edges. Here's a mockup of an origami-ish layout with a recess for the air flow.
Using HEPA filter's built-in gasket, we've separated the electronics in non-airtight box.
We've also tried snap-joints on edges, which didn't work reliably for thin stock.
With a shop vac and a heat gun we molded the interior, providing the rigid frame for the filter and the space for air flow
We've also tried different plastics and settled on 1mm PETg - it's way easier to vacuum form, bends by hand without breaking and cuts nicely on a laser.
The box contains a HEPA filter, a 12V fan, and 3 cell 18650 Li-ion batteries along with a BMS circuit. We've tested the setup work for over 10 hours which is more than enough for a working day.
Here's a mock-up of the electronics. At first we used cheap charge indicator modules but that wouldn't be as readily available as the rest, so we set out for a custom PCB.
We've designed a circuit with a speed controller and charge indicator with Arduino Nano as a controller, but found the soldering part too unreliable and time-consuming. We are now looking for an alternative solution.
This is the design so far. The filter fits inside and is held tightly with a plastic frame. Holes are sealed with hot glue.
A small number of units was produced and given out to three local hospitals to test.
We worked through several iterations, starting with a rough 3d model. We went for one-size-fits-all approach.
Layers of plastic film tend to weld together when laser cutting. Developing that idea, we ran an offset contour with defocused beam to create a reliable seal, and focused the laser to cut the final shape. Later we found that technique used in a hackaday article.
It was extremely difficult to find nice looking non-transparent PE film, but we've found inexpensive polyethylene bags. Thickness between 100 and 200 microns works best for us.
The visor is attached with scotch tape. We found that natural rubber adhesive tape is most resistant to alcohol and can be sanitized multiple times.
The adjustable head band and visor are made of PETg plastic. The hose is a standard sanitary item, and we've found a similar size across multiple manufacturers.
We've decided to use an HEPA certified filter to provide a high level of protection. A vacuum filter was the cheapest solution, as custom-made units would cost at least twice as much.
We ran a series of tests with different fans and studied professional PAPR units. To get a good enough airflow we needed a static pressure of about an inch (25mm) in H20. So we've chosen a fitting blower fan and added three 18650 cells to get about 12V. At this point we used a charge indicator module and were searching for an affordable battery manager/charger.
The initial idea was to build a low cost protection without wearing something on your face.
Helthcare workers during the COVID-19 pandemic work long shifts, and anything attached to your mouth is annoying at least.
We've built the first prototype by surrounding a face shield with polyethylene film and attaching a PC fan on top. This has worked relatively well, but the shield is heavy and there is no real filtering.
There is definitely room for improvement.